The invention relates generally to a method for recovering rare earth constituents from a fluorescent material (phosphor), for example, from phosphor waste. More particularly, the invention relates to a method for recovering rare earth constituents from a fluorescent material by a chemical route.
A phosphor is a luminescent material that absorbs radiation energy in a portion of the electromagnetic spectrum, and emits energy in another portion of the electromagnetic spectrum. Phosphors of one important class are crystalline inorganic compounds of high chemical purity, and of controlled composition, to which small quantities of other elements (called “activators”) have been added to convert them into efficient fluorescent materials. With the appropriate combination of activators and inorganic compounds, the color of the emission can be controlled. Phosphors are widely applied in various systems or devices with an annual volume growth of approximately 5%. Major applications are in emissive displays, fluorescent lamps and cathode ray tubes (CRT).
Rare-earth doped phosphors (also referred to as rare earth phosphors) play a critical and indispensable role as fluorescent materials in lighting and display applications. Usually, rare earth phosphor based devices exhibit a relatively high efficiency. The common triphosphor blend of fluorescent lamps generate red light via the emission of trivalent europium, blue light via the emission of divalent europium, and green light via the emission of trivalent terbium. Other commonly used rare earths include yttrium, samarium, praseodymium, cerium, lanthanum and gadolinium. A blend of red, green and blue phosphors is typically used for white light emission in display devices and fluorescent lamps.
A large amount of waste phosphor material is recovered from manufacturing residues and disposed devices. The disposed phosphor waste is a potential source of rare earth elements that could be recovered. It is of ecological as well as economic interest to recover or recycle phosphor materials, and especially expensive rare earth elements, which are essential for many applications other than phosphors. Examples of the applications include fabricating different alloys, preparing rare earth magnets, and preparing various types of catalysts.
Most of the prior attempts at rare earth recovery have focused on discarded fluorescent lamps, or computer displays. A few attempts were also made for recovering rare earths from waste phosphors, by pneumatic separation, or by a chemical method. However, these approaches may not always be economically suitable, because of their cost-intensive complexity, and/or their time-consuming nature.
It would therefore be desirable to develop new methods for efficiently recovering rare earths from fluorescent materials—especially from phosphor waste.